1. Field of the Invention
The present invention relates to an electric control apparatus for auger type ice making machines, more particularly to an electric control apparatus for protecting the ice making machine from an excessive load applied thereto in operation.
2. Discussion of the Prior Art
As schematically illustrated in FIG. 6, a conventional auger type ice making machine incorporates an auger which is mounted for rotary movement within the cylindrical housing 012 of an evaporator 011 to which water is supplied to cause ice crystals to form on the internal freezing surface of the evaporator housing 012. As the auger is driven by an electric motor 013, the helical blade thereof scraps the ice crystals off the internal freezing surface of the evaporator housing 012 and advances the scraped ice crystals upwardly toward an extruding head 014. The ice compressed at the extruding head 014 is broken by a breaker blade and delivered as pieces of hard ice to an ice storage bin 015. The storage bin 015 has an opening arranged to permit the pieces of hard ice to move outwardly along an appropriate delivery chute attached thereto. If in operation the delivery chute is blocked up due to the pieces of hard ice accumulated thereon, the storage bin 015 will be fully filled with the pieces of hard ice delivered from the extruding head 014. As a result, the pieces of hard ice are frozen in the storage bin 015 to cause an excessive load acting on the auger. To eliminate such an excessive load acting on the auger, a pressure gauge 016 is provided to detect a pressure drop of refrigerant in the refrigeration circuit 010, and a hot gas valve 017 is disposed in a bypass line of the refrigeration circuit to be opened for dissolution of the frozen ice when the pressure drop of refrigerant has been detected by the pressure guage 016.
In Japanese Utility Model Publication No. 61-28999, there is disclosed such an auger type ice making machine as shown in FIG. 7, wherein an auger 022 is mounted for rotary movement within the cylindrical housing of an evaporator 023 to which water is supplied to be formed into ice crystals on the internal freezing surface 024 of the evaporator housing. In the ice making machine, ice crystals scraped by the helical blade of auger 022 is pushed upwardly toward a compression chamber 025, and the ice compressed at chamber 025 is broken by a breaker blade 026 and delivered as pieces of hard ice to move outwardly along a chute 027. In Japanese Patent Publication No. 56-40258, there is also disclosed such an auger type ice making machine as shown in FIG. 8, the construction of which is substantially the same as that of FIG. 7. In the ice making machine shown in FIG. 7 or 8, a movable plate 028 is arranged to be pushed up by the pieces of hard ice packed in the storage bin of the machine, and a normally open detection switch 029 is associated with with the movable plate 028 to deactivate the electric motor 021 for the auger when it has been closed by upward movement of the movable plate 028.
In operation of the ice making machine, the ice crystals in the evaporator housing are frozen in the occurrence of shortage or suspension of water supply to the auger 022. Such abnormal freezing phenomenon of ice crystals may not be avoided. To avoid the abnormal freezing phenomenon caused by the shortage of water supply, Japanese Patent Publication No. 57-41669 discloses an electric control apparatus for the auger type ice making machine which includes a water level detector arranged to detect the level of water in the evaporator housing thereby to deactivate the electric motor for the auger when detected an abnormal fall of the water level. To avoid the abnormal freezing phenomenon caused by suspension of water supply, Japanese Utility Model Publication No. 60-17655 discloses an electric control apparatus for the auger type ice making machine which includes a float switch disposed within a water tank in communication with the evaporator housing to detect the level of water in the water tank thereby to deactivate the electric motor for the auger and the compressor in the refrigeration circuit when detected an abnormal fall of the water level.
Under control of the hot gas valve described above, the pressure drop of refrigerant in the refrigeration circuit is detected after the ice crystals in the evaporator housing have been frozen. It is, therefore, impossible to avoid the occurrence of an excessive load acting on the auger and the abnormal freezing phenomenon caused by shortage of water supply. In the case that a constant pressure expansion valve is adapted to maintain the pressure of refrigerant in the refrigeration circuit at a predetermined level, the control of the hot gas valve may not be adapted. It is further apparent that the detection switch associated with the movable plate is useless to avoid the abnormal freezing phenomenon in the evaporator housing caused by suspension of water supply, whereas the water level detector is useless to eliminate an excessive load caused by the pieces of hard ice packed in the storage bin.